Back to EveryPatent.com
United States Patent |
6,263,726
|
Hubbell
,   et al.
|
July 24, 2001
|
Sidewall tensiometer and method of determining soil moisture potential in
below-grade earthen soil
Abstract
A sidewall tensiometer to in situ determine below-grade soil moisture
potential of earthen soil includes, a) a body adapted for insertion into
an opening in earthen soil below grade, the body having lateral sidewalls;
b) a laterally oriented porous material provided relative to the body
lateral sidewalls, the laterally oriented porous material at least in part
defining a fluid chamber within the body; c) a pressure a sensor in fluid
communication with the fluid chamber; and d) sidewall engaging means for
engaging a portion of a sidewall of an earth opening to laterally urge the
porous material into hydraulic communication with earthen soil of another
portion of the opening sidewall. Methods of taking tensiometric
measurements are also disclosed.
Inventors:
|
Hubbell; Joel M. (Idaho Falls, ID);
Sisson; James B. (Idaho Falls, ID)
|
Assignee:
|
Bechtel BWXT Idaho, LLC (Idaho Falls, ID)
|
Appl. No.:
|
884480 |
Filed:
|
June 27, 1997 |
Current U.S. Class: |
73/73; 73/152.05; 73/152.06; 73/152.17; 73/152.41 |
Intern'l Class: |
G01N 025/56; G01N 005/02; E21B 049/00 |
Field of Search: |
73/73,152.05,152.06,152.17,152.41,19.09
|
References Cited
U.S. Patent Documents
2878671 | Mar., 1959 | Prosser et al. | 73/73.
|
3043133 | Jul., 1962 | Richards | 73/73.
|
3049914 | Aug., 1962 | Richards | 73/73.
|
3871211 | Mar., 1975 | Tal | 73/73.
|
3898872 | Aug., 1975 | Skaling et al. | 73/73.
|
4068525 | Jan., 1978 | Skaling | 73/73.
|
4520657 | Jun., 1985 | Marthaler | 73/73.
|
Foreign Patent Documents |
1174635 | Dec., 1969 | GB | 73/73.
|
1454674 | Nov., 1996 | GB | 73/73.
|
Other References
James, M. L. et al., Applied Numerical Methods for Digital Computation,
(3rd), Harper & Row, NY, pp. 86-93.
|
Primary Examiner: Williams; Hezron
Assistant Examiner: Loo; Dennis
Attorney, Agent or Firm: Kirsch; Alan D.
Goverment Interests
CONTRACTUAL ORIGIN OF THE INVENTION
The United States Government has rights in this invention disclosed under
contract number DE-AC07-76ID01570 between the U.S. Department of Energy
and EG&G Idaho, Inc., now contract number DE-AC07-94ID13223 with Lockheed
Idaho Technologies Company.
Parent Case Text
This application is a division of application Ser. No. 08/376,165, filed
Jan. 19, 1995 now U.S. Pat. No. 5,644,947.
Claims
What is claimed is:
1. A tensiometer to in situ determine below-grade soil moisture potential
of earthen soil comprising:
a body adapted for insertion into an opening in earthen soil below grade,
the body having lateral sidewalls, the earthen opening having opposing
lateral sides;
a laterally oriented porous material provided relative to the body lateral
sidewalls, the laterally oriented porous material at least in part
defining a fluid chamber within the body;
a pressure sensor in fluid communication with the fluid chamber; and
sidewall engaging means for engaging a portion of a sidewall of an earthen
opening to laterally urge the porous material into hydraulic communication
with earthen soil of another portion of the earthen opening sidewall.
2. The tensiometer of claim 1 wherein the pressure sensor is mounted
externally to the body.
3. The tensiometer of claim 1 wherein the sidewall engaging means comprises
an inflatable bladder positioned laterally of the porous material.
4. The tensiometer of claim 1 wherein the sidewall engaging means comprises
a piston and cylinder assembly positioned laterally of the porous
material.
5. The tensiometer of claim 1 wherein the porous material has an arcuate
periphery corresponding in male size and shape to a female arcuate
periphery size and shape of a cylindrical earthen opening size for which
the apparatus is adapted.
6. The tensiometer of claim 1 further comprising a flexible suspension
support line operably connected to the body to lower and raise the
tensiometer relative to an earthen opening.
7. The tensiometer of claim 1 further comprising a rigid support rod
operably connected to the body to lower and raise the tensiometer relative
to an earthen opening.
8. The tensiometer of claim 1 wherein the pressure sensor is mounted
externally to the body, and the sidewall engaging means comprises an
inflatable bladder positioned laterally of the porous material.
9. The tensiometer of claim 1 wherein the sidewall engaging means comprises
an inflatable bladder positioned laterally of the porous material, and the
porous material has an arcuate periphery corresponding in male size and
shape to a female arcuate periphery size and shape of a cylindrical
earthen opening size for which the apparatus is adapted.
10. The tensiometer of claim 1 wherein the sidewall engaging means
comprises an inflatable bladder positioned laterally of the porous
material, and further comprising a flexible suspension support line
operably connected to the body to lower and raise the tensiometer relative
to an earthen opening.
11. The tensiometer of claim 1 wherein the sidewall engaging means
comprises an inflatable bladder positioned laterally of the porous
material, and further comprising a rigid support rod operably connected to
the body to lower and raise the tensiometer relative to an earthen
opening.
12. The tensiometer of claim 1 wherein the porous material has an arcuate
periphery corresponding in male size and shape to a female arcuate
periphery size and shape of a cylindrical earthen opening size for which
the apparatus is adapted, and further comprising a flexible suspension
support line operably connected to the body to lower and raise the
tensiometer relative to an earthen opening.
13. The tensiometer of claim 1 wherein the porous material has an arcuate
periphery corresponding in male size and shape to a female arcuate
periphery size and shape of a cylindrical earthen opening size for which
the apparatus is adapted, and further comprising a rigid support rod
operably connected to the body to lower and raise the tensiometer relative
to an earthen opening.
14. The tensiometer of claim 1 wherein the body comprises a flexible
lateral sidewall with the porous material being received therein.
15. The tensiometer of claim 1 wherein the body comprises a flexible
lateral sidewall with the porous material being received therein, the
porous material comprising a screen which substantially fills the fluid
chamber.
16. The tensiometer of claim 1 comprising a plurality of said bodies with
associated pressure sensors, the plurality of said bodies being
elevationally spaced from one another along a common sidewall engaging
means.
17. A tensiometer to in situ determine below-grade soil moisture potential
of earthen soil comprising:
A body having a lateral sidewall, wherein the body in operation is void of
any mounted pressure sensing device, and the body comprises a normally
closed pressure sensing device access port in fluid communication with the
fluid chamber,
A laterally oriented porous material provided along a substantial portion
of the body lateral sidewall, the laterally oriented porous material at
least in part defining a fluid chamber within the body.
18. The tensiometer of claim 17 comprising a plurality of said bodies, the
plurality of said bodies being elevationally spaced from one another along
a common inflatable bladder.
19. A method of monitoring soil moisture potential in below-grade earthen
soil comprising the following steps:
inserting a tensiometer into a below grade opening in earthen soil; the
tensiometer having a porous material, a fluid chamber in fluid
communication with the porous material, and a degassed liquid within the
fluid chamber;
laterally urging the porous material against a sidewall of the earthen
opening to effectively establish hydraulic communication between the fluid
chamber and the earthen material;
permitting the degassed liquid to permeate the porous material to cause a
change in pressure in the fluid chamber; and
determining the change in pressure within the chamber.
Description
TECHNICAL FIELD
This invention relates to tensiometers and to techniques for measuring soil
moisture potential using tensiometers.
BACKGROUND OF THE INVENTION
If moisture potential of soil can be accurately monitored, irrigation can
be controlled to optimize the rate of plant growth. One type of instrument
for measuring soil moisture potential is a tensiometer. A conventional
tensiometer comprises a sealed tube defining a chamber which is normally
completely filled with water, a hollow porous tip on one end of the tube,
and a vacuum gauge connected to the water chamber. The porous tip is
inserted in the soil, and establishes liquid contact between the water in
the tube and moisture in the soil surrounding the tip. Relatively dry soil
tends to pull water from the tube through the porous tip. However since
the tube is sealed, only a minute amount of water is actually withdrawn.
Accordingly, the water in the tube is placed under tension by the pulling
effect of the dry soil, thus creating a measurable subatmospheric pressure
in the tube. Higher moisture contents in the soil produce correspondingly
less vacuum in the tube, and completely saturated soil registers
substantially zero vacuum or atmospheric pressure.
Typical tensiometer constructions provide a tube or column of water which
extends from the porous tip to above grade. It will be apparent that the
deeper the porous tip is buried, the longer the column of liquid above it
will become.
Air presence in the water reservoir during tensiometric measurement is
undesirable. Air can enter the reservoir by diffusing through the porous
tip. More commonly, dissolved air present in the water that enters the
vessel comes out of solution in the reduced pressure environment of the
tensiometer. Eventually, the entire tensiometer would become filled with
air. This air will increase the time required to reach pressure
equilibrium because large volumes of water must move through the porous
tip to effect the mass transfer of air through the tip. Thus in order to
obtain accurate readings, the water and air are desirably purged
periodically from the tensiometer reservoir and replaced with degassed
water.
To facilitate purging of air from the tensiometer reservoir, a conventional
tensiometer is typically provided with a column of water connecting a
surface located pressure measuring device to the soil-embedded porous tip.
However, there is a physical limit to the length of a column of water
which can be supported by atmospheric pressure (about 1000 cm at sea
level), and the useful measurement range of the tensiometer is reduced as
the column of water above the porous tip is lengthened. The pressure
exerted by the column of water increases the pressure in the porous tip,
which in turn increases the apparent soil moisture tension recorded by the
above-surface pressure measuring device.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described below with reference
to the following accompanying drawings.
FIG. 1 is a diagrammatic side elevational view of a sidewall tensiometer in
accordance with the invention.
FIG. 2 is a side elevational view corresponding to that of FIG. 1, but for
a 90.degree. rotation of the tensiometer.
FIG. 3 is a longitudinal sectional view of an alternate embodiment of a
sidewall tensiometer device in accordance with the invention as positioned
within a borehole for tensiometric measurement.
FIG. 4 is a sectional view taken through line 4--4 of FIG. 3.
FIG. 5 is a longitudinal sectional view of an alternate embodiment sidewall
tensiometer apparatus in accordance with the invention.
FIG. 6 is a longitudinal sectional view of another alternate embodiment
sidewall tensiometer apparatus in accordance with the invention.
FIG. 7 is a diagrammatic side elevational view of another alternate
embodiment sidewall tensiometer apparatus in accordance with the
invention.
FIG. 8 is a side sectional view the FIG. 6 tensiometer apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This disclosure of the invention is submitted in furtherance of the
constitutional purposes of the U.S. Patent Laws "to promote the progress
of science and useful arts" (Article 1, Section 8).
In accordance with one aspect of the invention, a sidewall tensiometer to
in situ determine below-grade soil moisture potential of earthen soil
comprises:
a body adapted for insertion into an opening in earthen soil below grade,
the body having lateral sidewalls;
a laterally oriented porous material provided relative to the body lateral
sidewalls, the laterally oriented porous material at least in part
defining a fluid chamber within the body;
a pressure sensor in fluid communication with the fluid chamber; and
sidewall engaging means for engaging a portion of a sidewall of an earth
opening to laterally urge the porous material into hydraulic communication
with earthen soil of another portion of the opening sidewall.
In accordance with another aspect of the invention, a method of monitoring
soil moisture potential in below-grade earthen soil comprises the
following steps:
inserting a tensiometer into an earthen opening below grade in earthen
soil; the tensiometer having a porous material, a fluid chamber in fluid
communication with the porous material, and a degassed liquid within the
fluid chamber
laterally urging the porous material against a sidewall of the earthen
opening to effectively establish hydraulic communication between the fluid
chamber and the earthen material;
permitting the degassed liquid to permeate the porous material to cause a
change in pressure in the fluid chamber; and
determining the change in pressure within the chamber.
The sidewall tensiometer and method to in situ determine below-grade soil
moisture potential is described with reference to FIGS. 1 and 2.
Tensiometer apparatus 10 includes a body 12 which is adapted for insertion
into a bore in earthen soil below grade. Body 12 is elongated and has
surrounding lateral sidewalls 13. Body 12 is substantially hollow defining
an internal fluid chamber 26. An arcuate or curved laterally-oriented,
porous material 24 is provided relative to one of body lateral sidewalls
13, and in part defines a boundary of fluid chamber 26 within body 12. A
pressure transducer 30 is provided externally of housing 12, and
communicates with chamber 26 via a conduit 59. Accordingly in the
illustrated embodiment, pressure transducer 30 is mounted externally of
housing or body 12. An example transducer is Model ST2P15G1, having a
range of from +15 to -15 psig, sold by SenSym of Milpitas, Calif. It could
of course also be directly connected to sidewalls 13, or retained
internally relative to housing 26. A fill tube 61 extends outwardly of
housing 12, and communicates with fluid chamber 26. A sealing cap 62 is
provided to seal fluid chamber 26. An electric lead 34 would extend from
transducer 30 to the surface. Component 65 diagrammatically illustrates
either a flexible line or a rigid rod for utilization in raising or
lowering housing 12 relative to a borehole in which the apparatus will be
utilized for tensiometric measurements. Alternately, tensiometer apparatus
10 can be raised and lowered using the electrical leads.
To utilize such a device, fluid chamber 26 would be filled with a degassed
liquid via fill tube 61. Thereafter, body 12 would be inserted into a bore
or trench below grade in earthen soil. Porous member 24 would be laterally
urged against a sidewall of the earthen bore to effectively establish
hydraulic communication between fluid chamber 26 and earthen material.
Degassed liquid would permeate the porous material to cause a change in
pressure in fluid chamber 26, which would be monitored by pressure
transducer 30. Such a construction method provides an advantage of
obtaining tensiometric measurements via sidewall bore access as opposed to
hydraulic access within the bore at the base.
FIGS. 3 and 4 illustrate a reduction-to-practice tensiometer apparatus 10a
in accordance with an aspect of the invention. Like numerals form FIGS. 1
and 2 are utilized with distinctions and construction being indicated by
different numerals or a suffix "a". Body 12a is configured with a bottom
opening 67 (FIG. 4) which is sealable by means of a rubber stopper 69.
Such opening is utilizable to fill fluid chamber 26a with degassed fluid.
Porous material 24a in one of body sidewalls 13a preferably has an arcuate
periphery, as shown, corresponding in male size and shape to a female
arcuate periphery size and shape of the size of bore 16 for which the
apparatus is primarily adapted.
An inflatable bladder 70 is provided laterally of porous material 24a
against one of lateral sidewalls 13a of housing 12a. Such is preferably
adhered by an adhesive or other means to the outer portion of sidewall
13a. An inflation/deflation hose 71 extends outwardly of bladder 70 to an
above-grade location.
When positioning apparatus 10a within bore 16, bladder 70 would be
initially deflated and the apparatus then lowered to a desired depth
within the soil. Thereafter, bladder 70 would be inflated with a fluid
(either liquid or gas, or a combination thereof). Such causes the bladder
to engage a portion of a sidewall of bore 16 to laterally urge porous
material 26a into hydraulic communication with earthen soil of another
portion of the bore sidewall, as shown. Tensiometric measurements are then
determined after equilibrium is reached, as described above.
Alternate mechanisms might also be utilized for urging porous material 24a
against the sidewall of a bore. FIG. 5, by way of example only,
illustrates one such alternate construction 10b. Such illustrates in
diagrammatic form a piston and cylinder assembly 72 which is positioned
laterally of porous tip 24b for expanding the lateral expanse of the
apparatus for urging porous material 24b against the sidewall of the bore.
Another alternate embodiment 10c is diagrammatically shown in FIG. 6. Such
diagrammatically comprises a plurality of sensors adhered to one side of a
common inflatable bladder 70c at different elevations. This would enable
moisture potential to be measured at different elevations within the soil.
The sensors could be adhered to bladder 70c by velcro.
The above sidewall tensiometric measuring apparatus might of course also be
constructed without an attached pressure sensing member, and instead use
an accessible septum. For example, cap 62 (FIGS. 1 and 2) could comprise a
septum.
Yet another alternate embodiment tensiometer apparatus 10d is illustrated
in FIGS. 7 and 8. In this embodiment, a thin porous plastic sheet 24d is
combined with a non-porous acrylic or PVC backing sheet 77. An example and
preferred material for sheet 24d is wettable porous plastic (A-20 or A-40)
manufactured by FMC. Backing sheet 77 is configured to provide a void 78
within the device, which is completely filled with a porous material 83.
An example and preferred material is a plastic or fiberglass screen, or a
scrim material. Sheets 24d and 78 are adhered to one another in
fluid-tight communication via perimeter adhesive 79. A passageway 80
extends from the rear of non-pervious backing 77 to void 78, which is
filled with screen 83. A PVC fitting 82 having opening 80 extending
therethrough is provided against backing plate 77, and communicates with a
conduit 84. Conduit 84 branches to fluid communicate with a transducer
30d, and a fill conduit 86.
Suitable bore sidewall engaging means such as an inflatable bladder would
also be associated with the device, as described above. Such would be
inflated once the device were inserted within a borehole to urge or push
material 24d outwardly against the bore sidewall. The described materials
are sufficiently flexible to enable the apparatus to curve or bend to
conform to the general arcuate sidewall shape to provide intimate contact
with the sidewall. Thus, this embodiment provides flexible, lateral
sidewalls having porous material received therein which in this embodiment
substantially fills the void, and is capable of flexibly conforming to the
internal sidewalls surfaces.
In compliance with the statute, the invention has been described in
language more or less specific as to structural and methodical features.
It is to be understood, however, that the invention is not limited to the
specific features shown and described, since the means herein disclosed
comprise preferred forms of putting the invention into effect. The
invention is, therefore, claimed in any of its forms or modifications
within the proper scope of the appended claims appropriately interpreted
in accordance with the doctrine of equivalents.
Top